Hydraulic power steering systems for vehicles typically include a rotary valve having a torsion bar. The torsion bar is a thin rod of metal that twists when torque is applied to it. One end of the bar is connected to the steering wheel, and the other end of the bar is connected to a pinion or worm gear, so the amount of torque in the torsion bar is equal to the amount of torque the driver is using to turn the wheels. The more torque the driver uses to turn the wheels, the more the bar twists. The input from the steering shaft forms the inner part of a spool-valve assembly. As the torsion bar twists, ports in the spool-valve open and close to provide high pressure hydraulic fluid to the appropriate hydraulic line to provide power assist.
In order to provide for proper operation of the rotary valve, the torsion bar and pinion gear must be precisely aligned. Providing the required degree of alignment between the torsion bar and pinion gear may be time consuming and problematic.